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We just purchased a 48" ZLine range with 7 burners. The information about all this CFM is very confusing.

Do I really need a 1200 CFM hood?

Alaska Man
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Lori Lowry
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  • You did not tell us why you think you need a 1200 cfm hood. If you read that in the code used in you area OR the range manufacturers instruction, then YES. You certainly need a strong enough fan for that big range, better too large then to small. – Alaska Man Mar 21 '21 at 17:29
  • @AlaskaMan -- not if you're only cooking on it once in a blue moon you don't – ThreePhaseEel Mar 21 '21 at 17:32
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    Are you going to be cooking on this 48" range for 10h/day, 5-6days/week, 52wks/yr? – ThreePhaseEel Mar 21 '21 at 17:32
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    @ThreePhaseEel IF you burn something or create smoke on that once in a blue moon kitchen adventure then you will wish you had proper ventilation ;) (*I loath under powered, inefficient range hoods*) – Alaska Man Mar 21 '21 at 18:10
  • @AlaskaMan -- I'd rather have a 300CFM hood with really good capture efficiency than 1200CFM of ventilation that sucks on everything but what's above the range – ThreePhaseEel Mar 21 '21 at 18:42
  • I gotta agree with @AlaskaMan. I have a 48" viking range with a 1,200 CFM hood and believe me, it needs it. – George Anderson Mar 21 '21 at 19:32

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A 1200CFM hood has no business being in a 3ACH@50Pa house (or worse yet, a tighter one)

One common misconception among custom kitchen shoppers is that a large, commercial-style range such as the 48" brute you're looking at requires a range hood ventilation system fit for a restaurant environment. The reason why commercial hoods are the brutes they are is because they have to maintain an environment reasonable for OSHA while the underlying appliances are being used for 10 hours per day, 6 days each week, for all 52 weeks of the year.

Your range, though, will never see such a usage pattern, and thus can and should be vented with a more domestically sized hood fan, on the order of 300 CFM. This is because all range hoods suck air out of the house, and that air needs to come from somewhere. In old houses, it just came from random air gaps in framing and sheathing as well as around penetrations such as windows, pipes, and electrical boxes; in newer houses, though, we seal those gaps so that we can control the air we're bringing in.

However, that control depends on there being a good balance of air in and air out, and a big range hood sucking on the house disrupts the balance, depressurizing the house and sucking in any contaminants that might be in the soil, in outside air (sucking on a house in the South is a great way to have a humidity problem!), or coming from sources such as combustion appliances. As a result, the IRC sets an upper bound of 400CFM for range hoods unless you provide a make-up air supply that's interlocked with the hood's operation and dedicated to the range hood. Given that you can't run kitchen range hood exhaust through an HRV or ERV due to issues with grease fouling of heat exchangers creating a fire hazard, you're best off not bothering with a hood that requires makeup air supply.

However, this doesn't mean you should get a physically tiny range hood that sits way above the range, sucking pointlessly on the air at the ceiling! You want the actual hood to span the full width and depth of your range, with a decent overhang and a tall catchment "bowl", so that you get good capture efficiency, maximizing the utilization of the CFMs you have installed. Likewise, downdraft ventilation has no business being used in this situation.

ThreePhaseEel
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  • Everyone should knows that if you are running the unit in high or medium mode you need to provide make up air by opening a window nearby – Kris Mar 23 '21 at 15:43